About the Authors
Dipartimento di Matematica e Informatica, Università di Siena, Siena, Italy
Dipartimento di Informatica, Università di Pisa, Pisa, Italy
The authors have declared that no competing interests exist.
We warmly thank the referees for their invaluable suggestions and comments. DC and RM conceived and designed the experiments. DC performed the experiments. DC, PD, and RM analyzed the data and wrote the paper.